A conceptual process for separating 4-morpholinepropanesulfonic acid (MOPS) from its aqueous solution was developed on the basis of the experimental solid-liquid equilibrium (SLE) data of MOPS + water and MOPS + methanol. In MOPS + water, a eutectic point was exhibited on the liquidus line and metastable ice was formed at lower temperatures. Due to the poor solubility of MOPS in methanol, methanol was found to be a suitable solvent to removed the residual water adhered to the crude MOPS crystals. The results from data correlation showed that the nonideal phase behavior of these two binary systems could be represented satisfactorily by the NRTL activity coefficient model.